Since a heater having Molybdenum Disilicide (MoSi2) as its principal component possesses superior oxidation resistance characteristics, it has been placed on the market from around 1950 to 1960 as an ultrahigh temperature heater to be used particularly in an atmospheric or oxidizing atmosphere, and it is still being used today for various purposes. This heater, as its principal component, contains 70 wt % or more of MoSi2.
Conventionally, a heater employed in various fields such as the glass industry or for ceramics calcination has a shape in which a heating part (moreover, a “heating part” usually means the portion of the heater having a small diameter (excluding terminal parts) that mainly generates heat during energization) forms a single U shape (2-shank shape) and is mounted by being suspended from the ceiling or sidewall of the furnace, whereby the maximum temperature during use of such furnace reaches 1700 to 1850° C.
In recent years, pursuant to the miniaturization of semiconductor devices, reduction of device manufacturing time and energy conservation, heaters having MoSi2 as its principal component are now being used in semiconductor manufacturing devices such as single crystal growth furnaces and diffusion furnaces in which metal heating elements were conventionally employed.
A heater having MoSi2 as its principal component possesses superior heat resistance characteristics and is capable of enduring a surface load of approximately ten times that of metal heating elements, and further possesses a significant characteristic in that it is capable of rapid heating and temperature rising.
Generally speaking, a heat treating furnace employed in semiconductor manufacturing devices is demanded of extreme high-precision temperature characteristics such as stringently controlling the temperature distribution within the furnace.
As a heater having MoSi2 as its principal component, generally employed is a U-shaped heater in which terminal parts are welded to both ends of a U-shaped heating part as shown in FIG. 5. The U-shaped heater 21 shown in FIG. 5 is structured of a heating part 22, a welding part 23, a grip (terminal) part 24, and an electrode part 25.
Nevertheless, since the terminal parts have a greater temperature reduction in comparison to the heating part, in a furnace requiring precise temperature control as described above, a (multi shank) heater has been proposed in which a plurality of U-shaped heating parts are connected in order to reduce the terminal parts.
With the shape of this type of multi-connected heater, since the number of terminal parts penetrating in and out of the furnace will decrease, heat loss released from the terminal parts can be reduced, and may have a certain effect in ensuring the uniform temperature within the furnace.
Nevertheless, in order to dispose a heater in an arc shape throughout the inside of a heating furnace or the like, it is necessary to bend the heater, which is planimetrically joined in a waveform, in an overall arc shape. In order to bend a heater having MoSi2 as its principal component, it is necessary to heat it to a high temperature of roughly 1500° C., and, since it is already joined in a waveform, there is a problem in that it is extremely difficult to make this into an arc shape, and it is difficult to manufacture a high precision heater.
Further, when the joining is not accurate or sufficient, there were accidents where the welded portion would rupture.